The present invention relates to a process for making glycol esters by a vapor phase oxidation and esterification carried out in the presence of a heterogeneous tellurium-based catalyst.
Ethylene glycol is largely produced at present by hydrolysis of ethylene oxide derived either from ethylene chlorohydrin by dehydrochlorination or from the catalytic oxidation of ethylene.
In recent years, processes have been developed whereby ethylene has been oxidized and esterified by reaction with molecular oxygen in the presence of an acetic acid solution containing a dissolved variable valence metal compound catalyst and a halogen or halide solubilizing agent or promoter, usually a bromide or chloride, at moderately elevated temperatures. Compounds of metals such as selenium, tellurium, vanadium, manganese, iron, chromium, and copper have been used as dissolved homogeneous catalysts in such liquid phase acetoxylation processes. The mono- and diacetates of ethylene glycol thereby produced are subsequently hydrolyzed by any of several known processes to produce ethylene glycol or they can be converted to vinyl acetate by pyrolysis. U.S. Pat. Nos. 3,668,239; 3,715,389; 3,770,813; and 3,985,795 are representative of those describing the oxidation-esterification or acetoxylation reaction.
The liquid phase acetoxylation processes for making glycol acetates are relatively efficient, but they have a number of serious practical disadvantages. These include the need for heavy pressure reactors, the use of expensive corrosion resistant materials because the acetic acid-halide reaction stream is highly corrosive, the necessity for handling large volumes of recycle streams, and the difficult separation of an often toxic dissolved metal catalyst from the product. There is need for an alternate approach that would avoid at least some of the more serious disadvantages.